In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on.
In a third-generation system, a transmission rate of maximum approximately 2 Mbps can be achieved on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink, by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, with the UMTS network, successor systems of LTE are also under study for the purpose of achieving further broadbandization and higher speed (for example, “LTE-Advanced” (LTE-A)). For example, in LTE-A, there is a plan to expand the maximum system band for LTE specifications, which is 20 MHz, to approximately 100 MHz.
Also, in a system of the LTE scheme, a MIMO (Multi Input Multi Output) system is proposed (see, for example, non-patent literature 1), as a radio communication technique to transmit and receive data by a plurality of antennas and improve the data rate (spectral efficiency). In the MIMO system, a plurality of transmitting/receiving antennas are provided in the transmitter/receiver, so that different transmission information sequences are transmitted from different transmitting antennas at the same time. Meanwhile, on the receiver side, taking advantage of the fact that fading variation is produced differently between the transmitting/receiving antennas, it is possible to increase the data rate (spectral efficiency) by separating and detecting the information sequences that have been transmitted at the same time.
Now, in recent years, vertical sectorization (VSEC) has been gaining popularity as a technique to secure communication capacity in a radio communication system. For example, a proposal has been made to improve the throughput of each cell by outputting a plurality of beams having varying beam angles (tilt angles) with respect to horizontal directions from an antenna apparatus, and setting the tilt angles of the beams in accordance with the conditions of radio base stations (see, for example, non-patent literature 2).